In conventional heap leaching of copper sulfide containing minerals (including chalcopyrite ores), mined ore is stacked into heaps, aerated through direct injection of air via aeration pipes extending into the heap and/or by natural convection through exposed areas of the heap, and irrigated with an acid solution for extraction of copper into solution. The copper is subsequently recovered from the acid solution by a range of recovery options including solvent extraction and electrowinning (SX/EW), cementation onto more active metals such as iron, hydrogen reduction, and direct electrowinning. The acid solution is regenerated and recycled through the heap to leach more copper from the ore in the heap. The ore in the heap may comprise agglomerates of fragments of ore. Leaching may be assisted by the use of microorganisms.
Generally, heap and dump leaching (hereinafter collectively referred to as “heap leaching”) provide lower metal recoveries than other metallurgical process options for recovering copper from copper-containing ores, such as milling and flotation that produces copper-containing concentrates that are then smelted to produce copper metal.
Consequently, heap leaching tends to be reserved for lower grade ore types that have at least a proportion of readily recovered copper, but where crushing/milling costs per unit of copper (or copper equivalent—i.e. when taking into account by-product credits from, for example, gold and silver) are too high to support a concentrator approach, or where mineral liberation and other characteristics (e.g. arsenic content) will not support production of directly useable or saleable concentrates.
Standard best industry practice is to use agglomerates of mined and thereafter crushed ore fragments in heaps. Typically, the mined ore is processed through multiple crushing steps, namely primary and secondary crushing steps, and in some instances tertiary crushing steps, and the crushed ore fragments are agglomerated in an agglomeration step, typically with the use of an acid.
The invention is concerned particularly with leaching mined and crushed and agglomerated ore fragments that contain chalcopyrite.
It is known that it is difficult to leach more than 20-40 wt. % of copper from chalcopyrite. The low copper recovery is often thought to be associated with the formation of a passive film on the surface of chalcopyrite.
The invention makes it possible to achieve higher recoveries of copper from chalcopyrite in ore fragments.
The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.